Used American batteries being recycled in Mexico using crude methods expose workers and residents to dangerous levels of toxic lead, environmentalists say.

Domestic U.S. recycling has become more difficult and expensive because of strict new Environmental Protection Agency standards on lead pollution, leading some companies to send the work -- and the danger -- to countries with lower protection standards, The New York Times reported Friday.

About 20 percent of spent American vehicle and industrial batteries are now being sent to Mexico for recycling to meet an exploding global demand for lead batteries crucial to cellphone networks, solar power arrays and automobiles.

Spent batteries can contain as much as 40 pounds of lead, which can interfere with neurological development in children and cause health problems in adults.

When batteries are broken for recycling, the lead can be released as dust and, during melting, as lead-laced emissions.

While Mexico does have some regulation for smelting and recycling lead, the laws are poorly enforced, experts said.

"If we export, we should only be sending batteries to countries with standards as strict as ours, and in Mexico that is not the case," said Perry Gottesfeld of Occupational Knowledge International, a San Francisco group devoted to reducing lead exposure.